The present invention relates to devices for measuring tire tread wear. More specifically, the present invention is a device for determining the tread profile by electro-optical measurements so that tread wear can be quantified.
Tire treads are defined by a number of grooves or channels cut into the peripheral portion of the tire. The treads are the portions of the periphery that come into contact with the road.
Tire treads give tires traction in cornering and stopping. Tire treads, however, wear during the course of use. Eventually, treads wear to the point where their ability to provide traction is compromised and the tire needs to be replaced or recapped.
Because tire treads wear slowly, and the amount of wear from day to day or week to week is imperceptible, frequent checking is unnecessary. Yet, unless a tire is checked for the depth of its treads at some reasonable internal, an excessively worn tire can be overlooked. Checking tire tread depth at intervals can allow a reasonably prediction as to when the tire will need to be replaced. Furthermore, such a prediction cannot be made, and, indeed, the amount of tread remaining can be difficult to quantify, without a measurement.
Many states have requirements about the condition of the treads of a tire and require the replacement of tires when they become excessively worn. Fleet managers may have their own internal requirements for replacement of tires that are worn based on tread depth or after a specified number of miles. Simple gauges or rulers are simply not accurate enough. Accurate measurement of tire tread depth is difficult to do without removing the tire and measuring the tread with special electro-optical measuring devices. See for example, the patents of Sube et al issued Sep. 21, 1993, U.S. Pat. No. 5,245,867, and Dory et al, issued Oct. 5, 1993, U.S. Pat. No. 5,249,460. In order to obtain an accurate measurement, the tire is suspended so that it is not engaging a surface. These devices are expensive and require a good deal of time and effort for checking the depth of the tread of a single tire. However, there remains a need for accurate tire tread depth measurement that does not have the defects of the prior art and that measures the profile of the tire tread so that tread depth ran be quantified.
According to its major aspects and briefly recited, the present invention is a probe for measuring the profile of a tire tread. A tire tread profile is a two-dimensional plot of the distance from each point on a fixed reference line running across the tire from side to side to the nearest point on the tire surface. This plot will show the differences in the distances to the line for the treads and the channels and thus the amount of wear on the treads. The hand held probe comprises a housing with a slit formed parallel to its major axis, a handle attached to the proximal end of the housing, a range finder mounted inside the housing in such a way that it can traverse much of the length of the tube while directing light from a laser through a window mounted over the slit, and a bracket that is carried near the proximal end of the tube to enable the user to hold the probe in position against the tire. The output from the device is via a computer port proximate to the handle or an IR or RP transmitter from the end of the handle. Power is supplied to the device by batteries in the handle.
The housing of the probe is placed against the tire with the slit and its window facing the tread. Preferably, the housing has an concave arcuate portion formed therein to define two edges of the housing that can act as supports on either side of the window to rest against the tire. When the device is pushed laterally toward the near side of the tire until it engages the tire, the device is then stabilized and in position to make a measurement. With the housing thus in position, the reference line with respect to the tire is set. The device is activated by pressing an xe2x80x9conxe2x80x9d button, causing the range finder to determine the distance from the range finder to the tire as the range finder slowly traverses the length of the housing. The distance dataxe2x80x94in terms of x and y coordinatesxe2x80x94is fed to the computer via either the computer port on the proximal end of the housing or the IR or RF window on the end of the handle. The computer can display the distance to the tread and to channels between treads as output, thus displaying the profile of the tire. A compute suitably programmed with local tread requirements can also determine if the tire is acceptable or not.
An advantage of the present device is its simplicity of use. The bracket and arcuate housing make it easy to position against the tire so that it is stable. The computer port that supports data transmission to a computer make the results of the measurement quickly available to the user via any computer.
Another advantage of the present invention is that it provides a tire tread profile rather than a series of single distance measurements. The profile of a tire provides more information than any single measurement and is a more reliable indicator of tread wear than a series of individual measurements, and quicker to obtain.
The IR or RP window in the base of the handle is still another feature of the present invention. This window makes it possible to avoid use of a cable when operating the present handheld tire tread profiler.
Other features and their advantages will be apparent to those skilled in the art of tread depth measurement from a carefull reading of the Detailed Description of Preferred Embodiments accompanied by the following drawings.